7. Project Abstract Accumulating evidence shows oncogenes/kinases that have been widely studied in cancers can be leveraged to treat traumatic brain injury (TBI). The evidence includes: 1) oncogenes/kinases (e.g., Src, ROCK, ERK, CDK, others) are activated after TBI; 2) activation of oncogenes/kinases not only cause neuronal death via cell cycle re-entry in mature neurons, but also mediate leukocyte infiltration and inflammation which results in BBB disruption after TBI; and 3) oncogenes/kinases inhibitors can improve TBI outcome, such as Src inhibitor (PP2), ROCK inhibitor (Y-27632), ERK inhibitor (PD98059), CDK inhibitor (Roscovitine), and others. In this grant application, the investigators hypothesized that elevating a single tumor suppressor microRNA (miR) to decrease multiple oncogenes/kinases will improve TBI outcomes. The investigators targeted tumor suppressor microNRA-125b (miR-125b) as a candidate for TBI therapeutics, because: 1) the pilot miR expression study showed that miR-125b is one of the top two miRNAs that significantly altered in blood after both TBI and ICH; and 2) miR-125b decreases multiple oncogenes (e.g., Mknk2, Alpk3, Neu1, Bap1, E2F, JNK, ERK, others) as predicted by miR-target algorithm (TargetScan), in addition to the oncogene Src which the investigators have previously shown plays an critical role in improving TBI outcome. The preliminary therapeutic studies demonstrate that miR-125b mimic (2.4mg/kg, intravenously, i.v.) and/or (0.24mg/kg, intracerebroventricularly, i.c.v.) can improve pathological outcome at acute stage (24 hr) and promote cognitive function at later times (11-15 days) after TBI. The investigators focus the mechanistic study on peripheral effects in this proposal, as i.v. treatment is more translatable to humans. Using whole genome sequencing, the investigators identify the top four miR- 125b target genes (Mknk2, Alpk3, Neu1, Bap1) that are decreased in blood after miR-125b mimic treatment after TBI. Note that all of the four top responsive genes are oncogenes/kinases. The preliminary mechanistic study data show: 1) miR-125b binds to the 3? untranslated regions (3?UTR) of Mknk2, Neu1 and Bap1; and 2) Morpholino Oligos (MOs)?miR125b?Mknk2 blocks the binding of miR-125b to 3?UTR of Mknk2. Moreover, they will prove that MO?miR125b?Mknk2/Alpk3/Neu1/Bap1 in vivo prevents miR-125b mimic-induced decrease of these target genes in blood cells (leucocytes, platelets), endothelium, and brain cells (neurons, astrocytes, microglia) after TBI, and thus blocks the therapeutic effects produced by miR-125b mimic after TBI. In summary, this proposal will show that miR-125b mimic has both peripheral and central effects to improve TBI outcome via decreasing miR-125b target oncogenes/kinases (Mknk2, Alpk3, Neu1, Bap1). This study will contribute to the literature of oncogenes/kinases pathophysiology in the TBI field. The combined use of i.v. miR-125b mimic and liposomes to treat TBI in rats is novel, and can be translated to treat human TBI.